Tire pressure switch unit



L. GERACK EF AL TIRE PRESSURE SWITCH UNIT Aug. 29, 1950 5 Sheets-Sheet 1 Filed May 9, 1947 Inventors Lester Gemci Angela Pablovich Aug. 29, 1950 L. GERACI El AL 2,520,241

TIRE PRESSURE swmcn UNIT Filed May 9, 1947 :s Sheets-Sheefn 2 [mm/tors Lesfer Geraci Ange/0 Pablovich Aug. 29, 1950 L. GERACI ET AL TIRE PRESSURE SWITCH UNIT Filed May 9, 1947 3 Sheets-Sheet 3 S m e l n I r m I Ih 0 A Mk V am a r 6P 3 9 o e I L e 0 g o n w J: A Q l l 2 I 0 9 M 9 m 2 I g F 6 8956 l 8 8 HAHN 9 0 78 8 7 3 9 H 9 6 0 w 0 2 GIL H w L? in I M m 6 7/ I 2 W w W 2 I m m l 9 Patented Aug. 29, 1950 TIRE PRESSURE SWITCH Lester Geraci and Angelo Pablovich, New Orleans, La., assignors of twenty-five per cent to Peter Note, and twenty-five per cent to Frank Noto,

both of New Orleans, La.

Application May 9, 1947, Serial No. 747,078

' 2 Claims. 1

This invention relates to a signal device for warning the operator of a vehicle upon which the device is installed of the condition of the tires of said vehicle, and more especially, when the same are deflated or under-inflated.

The object of the invention is to provide a signal system including certain visual signals, such as lights, or other signals which may be audible signals, connected to each tire of the vehicle and operated by the pressures in each individual tire, to indicate the condition of the air pressure therein and especially when the same is below normal required for the vehicle and load as normal operatin pressure, and which is designed to close a circuit to the signal when the pressure is below normal, so as to indicate to the driver or operator of the Vehicle when a tire is deflated or the internal pressure thereof is below normal operating pressure by an individual signal for each tire, so that proper steps can be taken to properly inflate the tire or repair the same, thereby avoiding accidents.

Another object of the invention is to provide a signal device for each wheel and tire, including a switch associated with each wheel and operated by the pressure within the tire to close a circuit to a signal on the dash, to indicate by means of a light or direct reading of such pressure due to a deflated condition of a tire, so as to indicate which tire is under-inflated and needs attention, and which includes a source of electrical energy or battery connected in circuit with the switches of each wheel for independent operation according to the pressure in each tire independently and selectively controlled, said circuit being grounded to the frame of the automobile or truck and operative in connection with single or dual wheels and tires, as well as of simple construction involving a minimum number of parts which can be easily installed and serviced, while requiring little servicing once installed for use.

Another object of the invention is to provide a signal device which includes a plurality of signals or pilot lights on an instrument panel operative in connection with each tire so that the operator will know which one is below normal inflation, or which operates in connection with an ammeter and a carbon pile rheostat, to vary the amount of current passing to the ammeter according to the pressure within a tire, and consequently the pressure exerted thereby to control the variable resistance of the carbon pile and the flow of current to the ammeter, ac-

cording to the degree of pressure in the tire,

whereby, in eithe instance, a warning will be given to the driver or operator so that a defective tire may be immediately taken care of.

Other objects and advantages reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings formin part hereof, wherein like numerals refer to like parts throughout, and in which:

Figure 1 is a sectional view showing a wheel of an automobile equipped with a signal device operating switch and circuit arrangement in accordance with the invention.

Figure 2 is a sectional view taken on the line 2-2 of Figure 1.

Figure 3 is an enlarged sectional view taken on the line 3--3 of Figure 1.

Figure 4 is a transverse sectional view taken on the line 4-4 of Figure 3.

Figure 5 is a detail elevation of a pressure contact piston employed in connection with the wheel switch.

Figure 6 is a diagrammatic view showing the circuit applied to an automobile having single front and rear wheels and tires.

Figure '7 is a sectional view showing the device applied to dual wheels such as used on trucks or trailers.

Figure 8 is an enlarged sectional view showing a contact switch employed in a dual wheel structure, as shown in Figure 7 and taken on the line 88 of Figure 9, with parts in elevation.

Figure 9 is a sectional View taken on the line 99 of Figure 8.

Figure 10 is a perspective view of a pressure piston and contact as employed in the switch shown in Figures 8 and 9.

Figure 11 is a diagrammatic view of the circuit arrangement with signals, for use in connection with dual wheels as employed in connection with a semi-trailer truck.

Figure 12 is a sectional view of a switch in the form of a carbon pile rheostat and associated ammeter with push buttons adapted to be associated with each wheel and tire for indicating the pressure therein in lieu of the switches shown in Figures 3 and 8 of the drawings.

Referring to the drawings in detail, and more especially to Figures 1 to 6, inclusive, each of the front and rear wheels I0 is shown with a rim I l, illustrated as of the beaded or clincher type having a reduced central annular portion or drop center [2, the rim receiving the usual pneumatic tire including a shoe or casing l3 and an inflated inner tube [4 having the usual infiating valve (not shown) The usual brake shoe flange or backing plate I5 is stationary with the usual front axle or rear axle housing and is associated with the usual brake drum it which revolves with the wheel including the outer disk I! over the outer portion or front {8 of the brake dru'in and associated, if desired, with a hub cap or flange :9 having an intermediate, inwardly extending annular flange 20, although the same may be of any preferred construction or conventional form connected to the brake drum by a conventional hub structure designed topperate upon the usual an spindle. secure to the flange or back plate [5 which supports the usual brake shoes operating in connection with 1 the drum !6, such as the internal expanding type, is an externally threaded terminal 21 e52- tends through an opening in said flange or plate l5 spaced radially from the center thereof one axis of rotation of the wheel and having an in- Side retaining flange 22-, well as insulated from the plate it through which it extends, by suitable fiber or other insulating washers 23 around the terminal and between the usage 22 and the plate, as well as between a retaining or look nut 24 threaded on the terminal at the inside to secure the terminal in 'posi ion against said plate The terminal 21 has a binding post 25, from which a wire z-e connected at it's terminal end the eto leads from each wheel to a signal, such as a light 2? of a series of four, depending upon the hum-=- her 'of wheels and tiles* ,'hbs'itioned on the or instrument panel of the vehiele. A long metal sleeve 28 is threaded or otherwise detaohably connected to the projecting outer end (if the terminal 2] forwardly bf the Henge 22 within the drum l6 and the outer end they be provided with a seat for receiving the i are ehd of a Spring 29, enclosed in the sleeve or enveloped therey, which furnishes pressure the eniarged inner end of a carton brush 30 which is held and projected outwardly of the outer end of said sieeve; "seemed with-i1 1 th'e wan I8 of the brake drum is a sl'ip 3i shaped to conform to said Wall and held in place through apertures therein in circular series, as shown in Figures "1 and 2, by means of screws '82 "entering threaded sockets in the ring and insulated from the brake drum by insulating washers Belts are connecting the brake s r-um $3 at the slip ring opening with the disk It of the wheel, retained by nuts A pin 3% is carried by the brake drum and rojects outwardly through an opening in the disk to line up the bolts and so that the wheel can only be placed in that position to line up the contacts "of the circuit new to be described.

Carried by each slip ring 31 is a metal strap or angle member '31 carrying a suitable bolt '38 clamped at the inside through the central por tion of the brake drum 1% and a Contact 39 at its outer end, insulated as shown at 4'0 from 'the brake drum in the same manner as the terminal 21 is insulated from the back or face plate 15 and the screws '32 are insulated from -the bralt'e drum If: at the portion l-8 thereof. Contact 39 makes contact with a contact '41 secured to and insulated from the wheel at the flange 20 by means of a bolt or binding terminal 42 and inshlated therefrom as shown at 43 with springs al" to keep the connection tight. From the bolt 'orsciew terminal 32, an electrical "connection or wire 4 3, connected at the terminal thereof and clamped in position by the nut on the bolt 'or terminal 42, extends through the wheel portions 4 20 and H through insulated washers or bushings 45 by which current is transmitted to a pressure unit and switch 58 by the Wire extending along the inside of the disk I! to the rim [2.

The pressure unit 46, as shown in Figures 1 and 3 to 5, inclusive, comprises a cylindrical casing 3 having an annular flange beveled outward- 1y, as indicated at 48, which extends through an opening in the drop center it of the rim H and is secured in position by means of bolts 4Q extending through apertures of opposite attaching flanges 56 projecting from the casing 41 secured ih threaded a ertures in the drop center of the rim and having the other two sides thereof fiattehed shown. A flexible diaphragm Si is secured over the enlarged inner bore of the casing 43 at the flange 68, by screws or the like, as indicated at 52, and contacts with the inner tube I'd so as to be acted upon by the pressure within said tube and tire. The diaphragm 5! on the inside acts upon the convex outer head 53 flanged to seat within an annular recess inside of the flange 48 at the outer end or the casing '41 and formed on the outer end of a piston or sleeve '54 which is movable radially within the casing 41 so 'as to operate freely within the bore thereof. This piston has a head slot 5'5 for operation by a screwdriver, and at one side is provided with a narrow longitudinal slot 53 and at the opposite side with an aligned, wider longitudinal slot 51 terminating" in an entrance portion or keyhole slot 53 curved laterally from the slot 57 and extending to the open, inner end of the sleeve or piston 54. The other terminal end of the wire as connects to a terminal contact 59 in the form of a binding post with suitable locking and adjusting nuts, and extends radially through the wall of the casing 4-1 irom which it is electrica'lly insulated, as indicated at 68, while the inner end thereof has an enlarged head 6i operating in the slot 5""! which is shorter than the slot 5%. The longer slot which is narrower than the 'slot 5? receives the reduced end 5-2 of alim-it-ing and stop screw 63 threaded through a radial lateral bore in the casing 41 and is cut to close tolerance so as to give a good fit for the reduced inner end 62 to avoid any side .play in the piston -54 and thereby prevent contact of the enlarged contact head Bl with the sides of the slot '51 but adapted to permit contact thereof with the ends of the slot 5! at the piston 54 when the piston travels its entire length and is limited in its movement by engagement of the head 61 with the ends thereof, especially the inner end, due to 4 under-inflation of the tire and inner'tube when the pressure has fallen below the desired or nor rnal operating pressure. A spring "6 is mounted within the piston to act on the flanged hea'd53 thereof, the outer end engaging the closed outer end of the piston and the inner end seating against an adjustment -screw 6 5 threaded through the reduced threaded bore at the inner end of the casing 41, to adjust the tension of the spring to the desired pressure for the tire and adapted to cause outward radial movement of the vpiston an engagement of the inner end of the slot 357 with the contact 6| when the pressure is below normal. In other words, when the pressure within the tire and inner tube is below normal, or that desired for running operation, the spring 64 will force the piston outwardly, the tension or the sprin 64 being set or adjusted by the screw so that the piston will travel outwardly from the cylinder and therein and will engage or touch 'the stop 62 and the contact 64 of the tersminn 59 to also serve as a stop as to th longi tudinal movement of the piston radially of the wheel and rim while the stop 62 prevents rotation thereof and engagement of the contact 6| with the sides of the slot 51 of the piston. This will complete an electrical circuit to the signal of the respective wheel and tire, inasmuch as each wheel or its rim is grounded to the frame, axle or body of the car, as indicated at 66 in Figure 6 of the drawings showing the diagram of the circuit for operating a separate signal 21 for each tire. In other words, the construction of each wheel and pressure unit and contacts therein is the same for all wheels, and a conductor 26 leads from each pressure unit and contact 46 and through the contacts and wire 44 to the terminal 25, to which the wire 26 is connected to extend to each signal 2'1,v which may be visual, such as a light, or audible or otherwise. The signals 21 are, in turn, connected to a common conductor or wire 61 and through a switch es, such as the ignition switch or otherwise, to control the circuit, and to a source of energy represented by the battery 69 of the car which is grounded to the automobile frame, as indicated at 18. In this way, the circuit to each pilot light or signal 21 is normally open until the pressure within the tire inner tube falls below the desired running pressure, when the circuit is closed through the engagement of the piston 54 with the contact BI, and the location of the pilot lights or signals 2! are such as to indicate the respective tire in which the pressure is too low, by operating its respective pilot light on the instrument panel or dash of the vehicle to be readily observed by the operator or driver, so that the vehicle can be stopped and the tire which is defective or in which the pressure is too low, attended to at once to avoid accidents. Thus, an instantaneous warning is given the operator when a tire is defective by reason of a leak, blowout or low pressure. To remove the piston 54 from the unit 45, the stop screw 63 is first removed to permit the piston to turn in the casing ll and by using a screwdriver in the groove or slot 55 of the piston head 53, and giving the same a half turn, the piston may be removed through the rim after removal of the tire or by detaching the unit 46 at the screws 49, by permitting the head 6! to pass through the entrance slot 58, thus permitting convenient and quick assembly and disassembly of the pressure and contact unit 48 while permitting the device to be produced in a sim le form at low cost.

In Figures '7 to 11, inclusive, the signal system is shown as applied to dual wheels of a semitrailer, tractor, bus or other automobile or vehicle using such system, in which the pressure units and signals operate in the same manner as described in connection with Figures 1 to 6, inclusive. In this form, the inner wheel is designated at H and the outer wheel at 12, having the rims l3 and the usual tires l2 and inner tubes id, as described in connection with Figure 1. The flange or stationary base or back plate mounting the brake shoes, and stationary with the axle M, is indicated at I5 and the drum at l6, as previously described, with the front portion or outer wall l8 for the inner wheel, to which the outer wheel is bolted, as indicated at 75, around the hub it, the cap of which is bolted in position, as indicated at ll, in a conventional manner. The rim may be of any usual construction employed in dual wheel structures. In this form, the wires 26 pass through the flange or base plate it at the insulated washers or'bushings l8 and 6 may be fastened to the axle housing, as indicated at 19, with similar brush arrangements mounted in U-shaped brackets fastened to the plate 15, as indicated at 8|, by means of apertured flanged seats on the legs or sides of the brackets extending within the drum and connected to terminals 25 with adjusting screws 2!, nuts 24, insulated washers or bushings 23, flanges 22 and cylinders or sleeves 23 enclosing springs 29 and similar carbon brushes 30, as described in connection with Figure 1. These brushes engage a similar slip ring 3! secured to the brake drum, except that, in this instance, the ring 3| is the inner of a pair of concentric spaced inner and outer rings, including the outer ring 3 i so that one brush 30 engages the outer ring 3 l while the other brush 39' engages the inner ring 3|, both secured to but insulated from the brake drum 1%, as indicated at 33, each of which is used to transmit current to its respective pressure and contact unit mounted upon the outer side of the lateral wall [8 of the drum it instead of at the drop center or reduced portion or" the rim as in Figure 1. Of course, the wires 25 and brushes 38 and 30' extend different distances radially of the brake drum flange or backing plate [5, to properly engage the slip rings 3! and 3! and the pressure units 46' are mounted on the brake drum at the front or outside to project from the inner wheel at the supporting disk I? with openings therethrough rendering them accessible through the outer wheel and disk of the inner wheel, as indicated at 32. The inner ring is used to transmit current to the inner pressure unit and contact 46', while the outer ring is used to transmit current to the outer unit provided for the outer wheel and its tire and inner tube. However, in this form, a short jumper or wire 84 is used to convey the current from its respective slip ring after extending through and being insulated from the drum portion Hi to which the units are bolted and from which they are insulated, as indicated at 85. The units are mounted on the brake drum instead of through th drop center of the rims, for the reason that trucks or buses carry a heavy flap inside the casing which is very thick and bulky and through which connection cannot properly be made between the pressure and contact units and the inner tubes of the tires. However, the units instead of being constructed as shown in Figures 3 to 5, inclusive, have the short wires or jumpers 84 connected to the terminals 59 of the contacts 60 with the enlarged heads 55 in the construction shown in Figures 7 to 10, inclusive. However, the construc-- tion of these units is the same as heretofore described, with the parts similarly numbered, except that in lieu of the flanged heads 53 of the pistons 54, the head 53' is the same diameter as the bore of the casing, cylinder or cup 47 and the flange 52 has the flexible diaphragm 5! disposed between it and against the head 53' of the piston 54' and a cap plate or head 86 bolted in position, as indicated at 8! through aligned openings is said head and said flange. Each cap plate or head 83 has a concave recess 88 cooperating with the recess flange 58 of the casing 41 at its open end, in which the flexible diaphragm 5| is adapted to flex or move, and a passage 39 leads centrally therefrom and radially so that pressure may act upon the flexible or rubber diaphragm 5| at the air chamber provided in the head 86. An angular pipe fitting 9-9 is detachably fitted or connected to the passage 89, as indicated at 9! and extended laterally through an opening 82 of the inner wheel and has on its :end an inflating valve 92 corresponding to the inflating valve of a tire. I?he fitting '93 has a branch 93 extending outwardly for connection with a flexible tmetal covered hose or conduit 5d, as by a coupling or nipple -95, rendering the same detachable, and connected or mounted with an interposed fastening or coupling 96 by which connection-is made to the inflating valves 91" of the respective tires and left on permanently because-of the special fittings '93 which makes it possible to gauge the pressures of the tires, inflate or deflate by useof the valves 92 in the ends of said fittings, in the customary manner.

The pressure and contact units 46' act in the same manner as the units 1% in that the air within the inner tubes of the tires acts upon the ,diaphragms 155' through the hose 9d and fitting 953, so that should the pressure in either tire be below normal or a leak or blowout occur, the y tire will be deflated, thus permitting the spring 643 to move the piston 5d outwardly against the diaphragm 51 and close the circuit by the engagement of the contact an with the said oylin der through the piston at the casing 47 which is rounded to the wheel and frame through the axle or housing, in the manner previously described in connection with Figure 6, and as indicated at 55 in saidfigure, as well as in Figure 11 showing the diagram of the circuit for use in connection with :dual wheels on a semi-trailer or truck, or the like. This circuit arrangement is the same as shown and described in connection with Figure 6,, except that the wiring connections are duplicated for each wheel and tire of the dual tire arrangement and for the single front wheels and tires to connect to each individual signal or pilot light 27 arranged on the instrument :panel or dash in :the respective ,order and .relationin which the tires are arranged on the vehicle. :Each connection 6? is duplicated for the respective lights, leading through the control switch or ignition-switch 681tothe source of electrical energy represented by the battery 6-9 and grounded as indicated at 3:0, in the same manner as shown and described in connection with Figure 6. In other words, the circuit is closed through the frame and each signal, upon the pressure and contact unit of each tire and wheel operated under pressure below normal or when deflated, by movement :of the respective pistons 51? or 5% into engagement with a contact fil to close the circuit through "the signal or .pilot light 1:27 connected therewith and through the switch '68 when closed, to the battery 69 and through theiframe or body of the car .or automobile to the respective wheels, through the axles or housings thereof, :at the units :mountedin the rims.

In the form ofthe-invention shown in Figure :12 of the-drawings-a pressure unit 26a is employed, ,which is interchangeable with the pressure unit shown-in Figure .8, although either :may be modifiedior-employment in the same manner as the pressure unit 45 shownin Figure 3 of theldrawings by removing the head or cap plate 86 and using eitherpiston 53or 53' engagingthe flexible diaphragmat the inner tube i i. The difference is .in the internal construction of the unit 46a, the system shown in-connection therewith being designed to indicate on the instrument panel or dash of the automobile, in the present instance, by a meter lpaneland pushbutton arrangement to show any amount of pressure atire mayhave by simply pushing a button on the ,panel in the cab of the vehicle, In this form, the cylinder housing or casing 47', as well as the diaphragm and the cap plate or head 88 bolted as at 87 to and through the diaphragm and flange 5c of the cylinder ,or housing 4?, is the same as previously described in connection with Figures 3 and 8., except that the cylinder or housing is shaped as shown in the latter figure, The pipe fitting Si and its connections, together with the inflating valve s2, is also the same and connected to the tires through the rim in the same manner, However, in lieu of the internal contact structure for closing a circuit to the signals or pilotlights 27 as previously described, a carbon pile rheostat :93 which will vary the current through the meter 99 arranged on the meter panel Hit in the cab .or on the instrument panel or dash by the varying pressure on thediaphragm 5i from the air pressure in the tire,:-is;employed. In this instance, the wire corresponding to the W1re226 of each tire is connected individually with a number of push buttons or other switches or contacts it] on the panel [06, connected to the ammeter 9B which may be calibrated in pounds pressure and is preferably a direct current meter. The meter is shown with the pointer Hi2 cooperating with thedial calibrations I63 to indicate pounds pressure in the tires. The number-and arrangement of thepush button contacts or switches NH corresponds to the number and arrangement of the tires on the vehicle, as shown in Figures-6 and ll, the latter arrangement being shown on the meter P nel i199. Thus, each wire 28 is connected to a pressure unit which is essentially a carbon pile rheostat, as indicatedat a to a terminal 104 through an insulating washer E65 around ,an opening at the adjacent end of thehousingfi'i' or cylinder forming the sameand has an enlargement or shoulder I06 on its inner end within said cylinder housing with an interposed metal washer ,lfll "between said shoulder or flan Mi d a ld d .fi er o in n l e H18 provid d wi i the y i d r hou in .including the end thereof .at the Washer liil, behind which the shoulder j 116 is provided inwardly or the housing cylinder within the insulating liner LE8 and also insulating the stem of the terminal 19.4 where it passes through theend wall of the housing, as indicated at MB. This assembly is held snugly bymeansroranut lit von the threaded endof the terminal .lll l iand whichpressesagainst the insulating washer 1,85, while a nut :I H clamps the ,terminalof thewireZB on the threaded terminal end of the binding post thus produced. Within the liner 498 are disposed a plurality of carbon washers H2 which are prevented by the liner .it8 fromcontacting with the metal of the casezorhousing -41 :and ,have their bores :correspending in diameter to the diameter of the shoulder 106 to receive therein i-ncontact with said shoulder, .a Bakelite or similar insulating sleeve Me on which the carbon washers H2 are mounted inconjunction with the shoulder H16 at andengagingthe closed end of the sleeve indicated at H4 and thus insulated therefrom at said shoulder. This p events a short circuit through the metalcaseor housing ii. A Spring I I5 is-disposed within the sleeve H3 so as to be encased within the Bakelite sleeve or tube of which the same is ,formed and ,a metal Washer .115 within the liner N38 is mounted on one end of the spring in connection with a radially-extending metal strip M! which extends between the flange at the-end of thehousing orcase 4'! and the flexible diaphragm and riveted to the metal washer, as indicated at H8, so as to be passed between the diaphragm and the case or housing upon clamping the head 86 in position by the bolts 81 with the bolt extending through the strip or strap H1, thus providing a conductor which will make a path for the current through the carbon washers which will ofier a variable resistance to the flow of the current. The spring H5 will help separate the carbon washers H2 when the pressure on the diaphragm 5| becomes less, the Bakelite case or insulating sleeve H3 preventing the spring H5 from forming a short circuit between the terminal I04 and the metal washer I H5. The outward appearance and size of this unit is the same as the unit described in connection with Figures 7 to inclusive, and substantially the same as that shown in Figure 3, and the mounting and hose connections will be the same as indicated in Figure 12. Thus, by operating any one of the individual push buttons or contacts IDI to the meter for actuating the pointer or indicator thereof, the push button switches which will be self-releasing will permit the inspection and checking of any individual tire by selecting the respective push button of the unit and tire to which it is connected so as to indicate on the calibrated dial in pounds pressure per square inch, the degree of pressure in any one tire or all of them successively, to indicate when they are under-inflated and need attention. Obviously, the operation of the ammeter 99 is dependent upon the resistance offered by the carbon washers to the flow of current, depending upon the pressure exerted against the same by the pressure within the tire through the flexible diaphragm 5i and the connections thereof with the fitting 9| at the passage 89 and chamber 88 through the fitting 90 and inflating valve 91,

while inflation of any tire may be had through the special valve 92 on said fitting. However, this device instead of operating automatically due to deflation or under-inflation of a tire tube will be manually operated by operating the respective push buttons Hll to select the different tires for indicating the pressure therein which controls the indication thereof through the pressure in the tire acting upon the carbon washers of the carbon pile rheostat of the pressure unit 45a and the resistance offered by said washers to the flow of current to the ammeter to indicate said pressure. The testing of the tires may be carried on periodically, or whenever occasion arises or inspection shows any indication of low pressure.

Thus, the device may be employed and readily installed on an automobile for use in connection with the wheels and tires thereof, to indicate the condition of the tires of said vehicle or automobile of any type having any number of tires, so that the pressure in the re pective tires may be determined instantly at all times. The device is of very simple construction and may be easily installed, in addition to requiring a minimum number of simple parts of economical construction, which will require little servicing once installed. However. access to all parts may readily be obtained and the units disassembled and assembled in a quick and convenient manner, in case any renewals or replacements are necessary.

While in the foregoing there has been shown 10 and described the preferred embodiment of this invention, it is to be understood that minor changes in the details of construction, combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as claimed.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. In a tire pressure indicator for an automotive vehicle having a wheel, a tire mounted thereon, an inflated pneumatic tube within the tire, and a rim having an opening therein; a pressure unit mounted in said opening secured to the rim, said pressure unit including a housing, a diaphragm closing one end of the housing and engaging the inner tube to be acted upon by the pressure therein, a piston movable in the housing, an adjustable resilient member acting upon said piston to force the same against the diaphragm, said piston having opposed slots therein, a stop engaging one of said slots to prevent turning of the piston in the cylinder, a contact having an enlargement movable in the other slot and spaced from the sides thereof to contact the ends of the slot, and means adapted to operatively connect said contact to a signal, whereby when the pressure in the tube is below normal, said piston will move outwardly to engage the contact at one end of the second slot therein.

2. In a tire pressure indicator for an automotive vehicle having a wheel, a tire mounted thereon, an inflated pneumatic tube within the tire, and a rim having an opening therein; a pressure unit mounted in said opening and secured to the rim, said pressure unit comprising a housing, a diaphragm closing one end of the housing and engaging the inner tube, a tubular piston movable in the housing having a convex head adapted to contact said diaphragm, an adjusting screw received in said housing and extending into said piston, a coil spring in said piston interposed between said screw and said convex head and nor mally urging the latter into contact with said diaphragm, a narrow longitudinal slot through one side of said piston and a wider, longitudinal slot through said piston diagonally opposed to said narrow slot, said wider slot including an arcuate entrance portion, a contact insulated from said piston and extending through said wider slot, a limiting screw carried by said housing and extending through said narrow slot to prevent side play in said piston, and means adapted to operatively connect said contact to a signal.

LESTER GERACI. ANGELO PABLOVICH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,294,923 Long Feb. 18, 1919 1,657,406 McGuire Jan. 24, 1928 2,033,424 Gieskieng Mar. 10, 1936 2,248,047 Addy et al. July 8, 1941 2,249,426 Jones et a1 July 15, 1941 2,314,965 Alava y Sautu Mar. 30, 1943 2,429,024 Jones Oct. 14, 1947 

